1. Field of the Invention
The present invention relates to improvements in the construction of a piezoelectric or electrostrictive actuator of bi-morph or uni-morph type used as or for a displacement-controllable element, an ink jet ejector, a VTR head, a switching element, a relay, a print head, a pump, a fan or blower, and other components or devices. The term "actuator" used herein is a member capable of transducing or converting an electric energy or signal into a mechanical force, displacement or strain.
2. Discussion of the Prior Art
Recently, an element whose displacement can be controlled has been widely used and increasingly needed in the fields of optics and precision positioning or machining operations, for example, for adjusting or changing an optical path length or the position of a member or component of a device, on the order of fractions of a micron (.mu.m). To meet this need, there have been proposed and developed various piezoelectric or electrostrictive actuators utilizing a piezoelectric or electrostrictive material such as a ferroelectric material, which exhibits the reverse or converse piezoelectric effect or the electrostrictive effect, in which the application of a voltage or electric field to such a piezoelectric or electrostrictive material produces a mechanical displacement.
Conventionally, the piezoelectric/electrostrictive actuator is structurally classified into a mono-morph type, a uni-morph type, a bi-morph type and a lamination type. The mono-morph, uni-morph and bi-morph types provide a relatively large amount of bending or flexural displacement or deflection or distortion owing to the transverse mode of converse piezoelectric or electrostrictive effect, namely, due to the strain perpendicular to the direction of the electric field produced upon application of a voltage. However these types suffer from inherent problems such as a small magnitude of a force generated, a low response speed, a low level of electro-mechanical conversion efficiency, and a low degree of operating reliability due to the use of an adhesive for bonding the component layers. On the other hand, the lamination type utilizes the longitudinal mode of converse piezoelectric or electrostrictive effect, namely, the strain parallel to the direction of the electric field produced by the applied voltage, and therefore assures a large magnitude of the generated force, a high response speed, and a high level of electro-mechanical conversion efficiency. However, the lamination type suffers from an inherent problem that the amount of displacement produced is relatively small.
Thus, the conventional piezoelectric or electrostrictive actuators have drawbacks as well as advantages.
U.S. Pat. No. 2,540,194 discloses a piezoelectric transducer or actuator of the mono-morph type, which uses a generally elongate piezoelectric slab, and electrodes in the form of strips formed on a surface or surfaces of the slab. The electrode strips extend in the direction of width of the slab and are spaced from each other at predetermined intervals in the direction of length of the slab. In the piezoelectric actuator disclosed in this patent, the application of a voltage to the electrodes causes a mechanical strain only in a portion of the piezoelectric slab which is adjacent to the surface or surfaces on which the electrodes are formed. Accordingly, the amount of flexural displacement or deflection or distortion of the slab, and the magnitude of a force produced by the piezoelectric slab are extremely small or insufficient. In this respect, it is noted that no piezoelectric material exists between the adjacent electrode strips, as viewed in the longitudinal direction of the slab.